A joint generally consists of two relatively rigid bony structures that maintain a relationship with each other. Soft tissue structures spanning the bony structures hold the bony structures together and aid in defining the motion of one bony structure relative to the other. Soft tissue such as ligaments, tendons, menisci, and capsule provide support to the bony structures. A smooth and resilient surface consisting of articular cartilage covers the bony structures. The articular surfaces of the bony structures work in concert with the soft tissue structures to form a mechanism that defines the envelope of motion between the structures. When fully articulated, the motion defines a total envelope of motion between the bony structures. Within a typical envelope of motion, the bony structures move in a predetermined pattern with respect to one another. In the example of the hip joint, the joint is a ball in socket joint that is inherently stable. The capsule and ligaments spanning the hip joint provide stability while the muscles provide motion.
The articular surfaces of the bony structures may become damaged by a variety of diseases, accidents, and other causes. A common disorder of joints is degenerative arthritis. Degenerative arthritis causes progressive pain, swelling, and stiffness of the joints. As the arthritis progresses the joint surfaces wear away, resulting in contractures of the surrounding soft tissues that provide stability to the joint. Moreover, progression of the disease process increases pain and reduces mobility.
Treatment of the afflicted articular bone surfaces depends, among other things, upon the severity of the damage to the articular surface and the age and general physical robustness of the patient. Commonly, for advanced arthritis, joint replacement surgery is necessary wherein the articulating elements of the joint are replaced with artificial elements commonly consisting of a part made of metal articulating with a part made of ultra high molecular weight polyethylene (UHMWPE).
A relatively young patient with moderate to severe degeneration of the hip joint is often treated with drug therapies. While drug therapies may temporarily provide relief of pain, progression of the disease, with resulting deformity and reduced function, ultimately necessitates surgery. Alternative treatments such as non-steroidal anti-inflammatory drugs and cortisone injections similarly provide only temporary relief of symptoms. Accordingly, there exists a need for a source of permanent relief of symptoms associated with moderate to severe degeneration of the hip joint.
In severe situations, surgery may be indicated in which the articular surface of one or more of the bones related to the joint is partially or entirely replaced with an artificial surface, as, for example, when the acetabular socket and femoral head are replaced with a prosthetic device including an UHMWPE bearing to resurface the acetabulum and a polished metal or ceramic femoral head mounted to a stem extending into the medullary canal of the proximal femur to replace the femoral head. Joint replacement surgery has become a proven and efficacious method of alleviating pain and restoring function of the joint.
Current methods of preparing the rigid elements of a joint to receive components as in joint replacement surgery involve extensive surgical exposure. The exposure must be sufficient to permit the introduction of drills, reamers, broaches and other instruments for cutting or removing cartilage and bone that subsequently is replaced with artificial surfaces. For total hip replacement, the acetabular articular surface and subchondral bone is removed by hemispherical graters, the femoral head is resected with an oscillating saw, and the proximal medullary canal is shaped with broaches. A difficulty with total hip replacement is that the invasiveness of the procedure causes significant intraoperative blood loss and extensive rehabilitation because muscles and tendons must be released from the proximal femur to mobilize the femur and gain exposure of and access to the acetabular fossa.
Conventional total hip arthroplasty is indicated for painful arthritis of the hip joint. The procedure involves exposing the hip joint through a large incision to provide the surgeon full visualization of the hip joint and the acetabular region and to provide access for surgical power instruments. In order to appropriately prepare the bony structures of the hip joint, the major muscles spanning the joint are commonly disrupted to gain adequate exposure of the joint. Steps of the procedure include removing the femoral head followed by reaming and broaching the proximal femoral canal to prepare a bony surface to support a hip stem. The stem is implanted and may be cemented in place, or press fit for bony ingrowth. The acetabulum is typically prepared using sequentially sized graters to remove cartilage down to bleeding bone. Once the acetabulum is prepared, an acetabular component is implanted, either by cementing in place or press fitting for bony ingrowth. Extensive surgical exposure is necessary to accommodate the bulk and geometry of the components as well as the instruments for bone preparation. The surgical exposure, which may be between six and twelve inches in length, may result in extensive trauma to the soft tissues surrounding the hip joint along with the release of muscles that insert into the proximal femur. The surgical exposure increases bleeding, pain, and muscle inhibition; all of which contribute to a longer hospitalization and rehabilitation before the patient can be safely discharged to home or to an intermediate care facility.
The prepared bony surfaces are technically referred to as the acetabular fossa, femoral canal and metaphyseal region of the femur. Prior to placing the final implants into the prepared spaces, a femoral trial, which may be the broach in some systems, is placed in the proximal femur along with a trial femoral head and neck, and an acetabular trial is placed into the acetabulum to facilitate trial range of motion and evaluation of hip stability prior to placement of the final total hip implants.
Devices for minimally invasive hip surgery that prepare the acetabulum to receive final total hip implants are known. Hemispherical graters driven with straight drive handles connected to a surgical drill have been used. However, soft tissue structures limited proper orientation of these devices leading to the development of curved drive handles used to avoid soft tissue interference. The resulting reamer device, while partially avoiding soft tissue structures, still required the surgeon to force the handle against soft tissue structures to gain proper orientation of the grater. In addition, such devices still required retraction of the proximal femur to provide access for the handle and grater to the acetabulum. Extensive distraction force is needed to displace the femur resulting in trauma to soft tissue structures because of the magnitude and duration of the force imparted.
An acetabular grater that rotates about an axis transverse to the drive handle longitudinal axis is known for preparation of the acetabulum to receive an implant. The reamer device includes a grater and a drive handle. The drive handle has a pivotable head to which the grater attaches. The grater is rotated about the pivotable head to reduce the grater profile for a surgical incision. Once in the acetabulum, the grater rotates normal to the drive handle during operation. The grater includes cutouts in the hemispherical shell to allow rotation over the drive handle. As with the straight and curved drive handles described above, a pivotable head drive handle interferes with soft tissue structures while preparing the acetabulum and requires distraction of the femur to allow access to the acetabulum.
Based on the foregoing, there exists a need for surgical methods and apparatuses that may be employed to gain surgical access to articulating joint surfaces, to appropriately prepare the bony structures, to provide artificial, e.g., metal or plastic, articular bearing surfaces, and to close the surgical site, all without substantial damage or trauma to associated muscles, ligaments or tendons. There also exists a need for a system and method that enables articulating surfaces of the joints to be appropriately sculpted using minimally invasive apparatuses and procedures. There exists another need for a surgical navigation system to guide the preparation of articular surfaces and to position the acetabular implant.